1. Field of the Invention
This invention relates to gas-cooled windings of dynamoelectric machines, and more particularly, to means for electrically and mechanically connecting stator phase leads to the phase coils of such windings.
2. Description of the Prior Art
In large inner-cooled turbine generators which utilize a gas such as hydrogen as the cooling medium, the stator winding is usually split to facilitate heat transfer with an inner-cooling duct heat exchanging system. A split conductor arrangement is constructed by joining a large phase lead with two smaller conductors in an overlapping arrangement. The phase lead and conductors are composed of multiple conductor strands which are arranged in columns, and the combined cross-sectional area of the smaller conductor strands comprising the split winding is equal to the cross-sectional area of the larger conductor strands which comprise the phase lead. The smaller conductors, which are joined with the larger conductor in the end turn region of the stator, are extended in a parallel arrangement with the inner-cooling ducts through axial stator slots. The coolant is circulated through the cooling ducts in direct thermal contact with the current carrying split phase leads. The split conductor cooling arrangement has made it possible to greatly increase the maximum capacities in large generators without exceeding the permissible limits of physical size.
In this type of construction high mechanical strength and good electrical conduction is required for the union of the split phase lead conductor portions. Good electrical conduction and mechanical strength are interrelated fundamentally upon two factors: contact area and contact pressure. The effective contact area relative to the cross-sectional area of the conductor is of great importance since it controls the resistance of the connection. It must remain uniform in size and not be affected by temperature changes or vibration. The contact pressure must be high enough so that adjacent conductor surfaces are pressed together with essentially all particles of the contact area being interlocked and free from insulating impurities. In general, the contact force should be great enough to produce a contact area which is equal to or greater than 1.5 times the cross-sectional area of the conductor. If the force holding the conductors together is too small, only the high points of the surface is touched and large currents passing through such a connection may develop heat and melt the metal at the high spots.
Proper contact pressure and contact area have been provided by a variety of prior art devices. Commonly used phase lead connectors include the pressure clamp illustrated in FIG. 7 of the drawing. This clamp, formed of copper, is rolled to obtain the dimensions necessary to enclose the conductors. The rolled clamp provides only an approximate fit, however, and gaps remain after the pressure clamp is positioned around the stranded conductor union. Since these gaps must be closed during soldering to insure proper contact area and contact pressure, a large compressive force is applied to the clamp and the clamp is crimped around the overlapping conductors.
Coil strands have been severely deformed and broken as a result of this crimping procedure. Also, considerable difficulty has been encountered in maintaining the required contact area and pressure throughout the expected life of the clamp connector. Furthermore, unbonding of the soldered connection has been found to occur during operation of the turbine generator at high stator load currents. This unbonding is caused by various mechanical disturbances such as vibration and temperature changes. Large mechanical forces are induced by changes in high flux concentration surrounding these phase leads in the end turn regions. Also, when the soldered connection is subjected to high temperatures which accompany a large current flow, the contact pressure at the union of the conductors is relaxed.
These problems stem directly from the lack of precision in the fitting of the pressure clamp about the conductor strands and in the lack of means for applying and maintaining uniform pressure across the overlapped conductor strands. It is, therefore, a principal object for the present invention to provide a connector having a conductor receiving region which may be accurately adjusted to provide a closely conforming fit and which also includes means for maintaining controlled, uniform contact pressure of sufficient magnitude to insure good electrical conductivity as well as mechanical strength.